The increased use of and reliance on communication networks to transmit complex forms of data, such as voice and video data, has resulted in a demand in the marketplace for more bandwidth. Thus, conventional communication architectures that use coaxial cables are being replaced with communication networks that use only fiber optic cable, since optical fibers can carry a greater amount of data.
Data service providers have long desired Fiber-to-the-home (FTTH) and Fiber-to-the-business (FTTB) optical network architectures. These network architectures are known for their improved signal quality, for the lower system maintenance that they require, and for the longer life of the hardware that is employed in such systems. Though in the past the use of the FTTH and FTTB architectures was considered cost prohibitive, research and development has resulted in improved, cost-effective optical network alternatives.
The passive fiber optic network (PON) is an example of an FTTH architecture that is used in the industry. The PON architecture includes of an all-fiber network (where fiber optic transmission is used from the data service hub to subscribers' homes). In one configuration, optical splitters are used to divide the downstream signal among a plurality of homes, with one or more fiber optic cables connecting each home to the splitter. In another configuration, individual fibers extend from the data service hub directly to individual homes. Though the PON architecture allows for an all-fiber network, several drawbacks remain that make it impractical to implement.
First, in order to overcome the limitations that exist in the number of times an optical signal can be divided with an optical splitter before that signal becomes too weak to use, the PON architecture usually requires too many optical cables to originate at the data service hub. Second, because there is no active signal processing disposed between the data service hub and the subscriber, the maximum distance that can be achieved between the data service hub and a subscriber usually falls within the range of ten to twenty kilometers.
Third, another significant drawback of the PON architecture is the high cost of the equipment needed at the data service hub. For example, many PON architectures support the full service access network (FSAN), which uses the asynchronous transfer mode (ATM) protocol. Complex and expensive equipment is needed to support this protocol.
Fourth, not only is the PON architecture expensive, but it does not lend itself to efficient upgrades. Rather, in order to increase the data speed of the network, conventional and traditional PON architectures require fiber and router ports to be added during an actual physical reconfiguration of the network.
Finally, conventional PON architectures typically only support speeds up to 622 Megabits per second in the downstream direction and maximum speeds of 155 Megabits per second in the upstream direction. The term “downstream” can define a communication direction where a data service hub originates data signals that are sent downwards towards subscribers of an optical network. Conversely, the term “upstream” can define a communication direction where subscribers originate data signals that are sent upwards towards a data service hub of an optical network. Such unbalanced communication speeds between the upstream and downstream communication directions (referred to as asymmetrical bandwidth) is undesirable because it severely limits the amount of information that can be transferred from a subscriber to a data service hub.
As a result of the drawbacks of the PON architecture discussed above, a conventional hybrid FTTH/hybrid fiber-coax (HFC) architecture is commonly used by many cable television systems. In this FTTH/HFC architecture, an active signal source is placed between the data service hub and the subscriber. Typically, a router is used as the active signal source. The router has multiple data ports that are designed to support individual subscribers. More specifically, an optical fiber connects each data port of the router to each subscriber. The connectivity between data ports and optical subscribers yields a very fiber-intensive last mile. It is noted that the terms “last mile” and “first mile” are generic terms used to describe the last portion of an optical network that connects to subscribers.
In addition to the high number of optical cables originating from the router, the FTTH/HFC architecture requires that the optical signals be converted to electrical, radio frequency signals before they are propagated along traditional coaxial cables to the subscriber. Because radio frequency (RF) amplifiers are needed between the subscriber and the data service hub (RF amplifiers are typically needed every one to three kilometers in a coaxial-type system), this adds to the overall cost of the system. Additionally, because the FTTH/HFC architecture merely combines an optical network with an electrical network where both networks run independently of one another, high maintenance costs can result.
An additional drawback to the FTTH/HFC architecture is that the router requires a protected environment that occupies a significant amount of space. More specifically, it requires an environmentally controlled cabinet that must house the router and related equipment at an optimum temperature. In order to maintain this optimum temperature, the environmental cabinet typically includes active temperature control devices for heating and cooling the cabinet. These cooling and heating units consume power and are needed to maintain an operating temperature in all types of geographic areas and in all types of weather.
Although another conventional hybrid fiber coax (HFC) architecture exists that employs an active signal source between the data service hub and the subscriber that does not require a temperature-controlled environmental cabinet (as described above), this active signal source merely converts optical information signals to electrical information signals. More specifically, the active signal source in the HFC architecture converts downstream optical signals into electrical signals and upstream electrical signals into optical signals. Thus, because the conventional HFC architecture relies upon coaxial cable to transmit the electrical signals in the last mile of the HFC network, it still requires numerous RF amplifiers on the coaxial cable side of the network in order to ensure sufficient signal strength.
Additionally, the conventional HFC architecture also requires additional communication devices to support the data signals that propagate along the optical fibers between the active signal source and the data service hub. For example, because the conventional HFC architecture typically supports telephony service, it uses equipment known generically as host digital terminal (HDT). The HDT can include RF interfaces on the cable side and interfaces to either a telephone switch or to a cable carrying signals to a switch on the other side. Similarly, the data service hub of a conventional HFC architecture can further include a cable modem termination system (CMTS). The CMTS provides low level formatting and transmission functions for the data transmitted between the data service hub and the subscriber.
In addition to a CMTS, the conventional HFC architecture at the data service hub typically includes several modulators, or miniature television transmitters. Each modulator can convert video signals received from satellites to an assigned channel (frequency) for transmission to subscribers. Additionally, signal processors and other devices are used to collect the entire suite of television signals to be sent to subscribers. Typically, in a conventional HFC architecture, up to seventy-eight or more such modulators or processors will exist with their supporting equipment to serve the analog TV tier. Similar equipment will be used to serve the digital video tier.
Because HFC architecture uses CMTS, it cannot support symmetrical bandwidth. That is, the bandwidth of the conventional HFC architecture is typically asymmetrical because of the use of the data over cable service interface specification (DOCSIS). The nature of the DOCSIS standard is that it limits the upstream bandwidth available to subscribers. This can be a direct result of the limited upstream bandwidth available in an HFC plant. This is undesirable for subscribers who need to transmit more complex data for bandwidth intensive services such as home servers or the exchange of audio or video files over the Internet.
Another variation of the conventional HFC architecture exists in the marketplace where the CMTS can be part of the active signal source disposed between the data service hub and the subscriber. Though this variation of the conventional HFC architecture enables the active signal source to perform some processing, the output of the active signal source in this architecture is still radio frequency energy and is propagated along coaxial cables.
Accordingly, there is a need in the art for a system and method for communicating optical signals between a data service provider and a subscriber that eliminates the use of coaxial cables and the related hardware and software necessary to support the data signals propagating along the coaxial cables. There is also a need in the art for a system and method for communicating optical signals between a data service hub and a subscriber that supports high-speed symmetrical data transmission. In other words, there is a need in the art for an all-fiber optical network and method that can propagate the same bit rate downstream and upstream between a data service hub and a network subscriber. Further, there is also a need in the art for an optical network system and method that can service a larger number of subscribers while reducing the number of connections at the data service hub.
There is also a need in the art for an active signal source that can be disposed between a data service hub and a subscriber that can be designed to withstand outdoor environmental conditions and that can be designed to hang on a strand or fit in a pedestal similar to conventional cable TV equipment that is placed within a last mile of a communications network. A further need exists in the art for a system and method for receiving at least one gigabit or faster Ethernet communications in optical form from a data service hub and partition or apportion this optical bandwidth into distribution groups of a predetermined number. There is a further need in the art for a system and method that can allocate additional or reduced bandwidth based upon the demand of one or more subscribers on an optical network. Another need exists in the art for an optical network system that lends itself to efficient upgrading that can be performed entirely on the network side.
In other words, there is a need in the art for an optical network system that allows upgrades to hardware to take place in locations between and within a data service hub and an active signal source disposed between the data service hub and a subscriber. Another need exists in the art for an optical network that can increase information traffic carried by optical waveguides to and from subscribers of the optical network.